This invention relates to a fuel supply control method for multi cylinder internal combustion engines, and more particularly to a method of this kind which is adapted to control the fuel supply to the engine immediately after termination of a fuel cut operation which is effected at deceleration of the engine.
In conventional fuel supply control methods of electrically controlling the quantity of fuel to be injected into an internal combustion engine, the fuel supply to the engine is generally interrupted (hereinafter called "fuel cut") while the engine is decelerating with the throttle valve fully closed, until the rotational speed of the engine drops below a predetermined rpm value, to thereby improve the fuel consumption of the engine. This predetermined rpm value at which the engine is recovered to a normal fuel supply-requiring condition from a fuel cut effecting condition is desirably set at a value as close to the the idling rpm (e.g. 750 rpm) of the engine as possible, for improvement of the fuel consumption of the engine.
However, the engine cannot promptly produce torque immediately after the termination of a fuel cut operation due to a time lag between the time fuel is supplied to the cylinders and the time combustion of fuel thus supplied takes place in the cylinders to produce torque, even if the fuel supply to the engine is started immediately after the engine speed has decreased below the above predetermined rpm value. Therefore, if the predetermined rpm value is set at a value substantially equal to the idling rpm, the engine speed can drop to a large extent, often resulting in engine stall, during the above time lag, i.e. from the time a fuel cut operation is terminated to the time torque is produced by the engine, when load-creating equipments such as power steering are operated with the clutch maintained in an off state during the fuel cut operation.
In order to avoid such engine stall caused by the operation of the load-creating equipments, the above predetermined rpm value employed to determine whether or not fuel cut should be terminated has to be set at a value much higher than the idling rpm of the engine, e.g. at a value of 1200 rpm. However, the use of such high predetermined rpm value hinders satisfactory improvement of the fuel consumption of the engine.